linux-kernel - Re: [PATCH] lib/test_kmod: Fix a use after free in register_test_dev

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Message-ID: <20210311130108.GS4332@42.do-not-panic.com>
Date:   Thu, 11 Mar 2021 13:01:08 +0000
From:   Luis Chamberlain <mcgrof@...nel.org>
To:     Lv Yunlong <lyl2019@...l.ustc.edu.cn>
Cc:     linux-kernel@...r.kernel.org
Subject: Re: [PATCH] lib/test_kmod: Fix a use after free in
 register_test_dev_kmod

On Thu, Mar 11, 2021 at 12:02:46AM -0800, Lv Yunlong wrote:
> In register_test_dev_kmod, it calls free_test_dev_kmod() to free
> test_dev. But free_test_dev_kmod() can't set the original pointer
> test_dev to NULL, because the test_dev was passed by it's value
> not reference.

Did you actually get a crash or something? If so can you supply the
actual log? If this is just an observation and you think this is an
issue, specifying that would help during patch review.

  Luis

> Signed-off-by: Lv Yunlong <lyl2019@...l.ustc.edu.cn>
> ---
>  lib/test_kmod.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/lib/test_kmod.c b/lib/test_kmod.c
> index 38c250fbace3..aa8a2a563d7e 100644
> --- a/lib/test_kmod.c
> +++ b/lib/test_kmod.c
> @@ -1124,7 +1124,6 @@ static void free_test_dev_kmod(struct kmod_test_device *test_dev)
>  		free_test_dev_info(test_dev);
>  		kmod_config_free(test_dev);
>  		vfree(test_dev);
> -		test_dev = NULL;
>  	}
>  }
>  
> @@ -1149,6 +1148,7 @@ static struct kmod_test_device *register_test_dev_kmod(void)
>  	if (ret) {
>  		pr_err("could not register misc device: %d\n", ret);
>  		free_test_dev_kmod(test_dev);
> +		test_dev = NULL;
>  		goto out;
>  	}
>  
> -- 
> 2.25.1
> 
>